View Full Version : Fastest way home?
JJ Sinclair[_2_]
June 17th 13, 07:32 PM
The last day at Montague was spectacular, probably the best soaring day I have ever seen! After flying 7 assigned turn-points in an 8-turn (3hr) MAT, I was 45 miles out with 3500' over MC-3 glide home and the SN-10 said I would be 4 minutes over the 3 hr minimum time. My stats page told me I was doing 70 mph so far after cruising 80 knots all day long.
Question: Is it faster to raise the MC to 4 or 5 and come home at 90'ish (monitoring time and altitude required), probably bringing my time remaining down to zero..............Or should I use my excess altitude to select another turn-point adding 10 more miles to the total distance and continue to cruise at 80 and be overtime about 13 minutes?
I did the latter and got 73.5 mph (236 miles), but I have a sneaking feeling I should have done the former.
JJ
JJ Sinclair[_2_]
June 17th 13, 08:32 PM
On Monday, June 17, 2013 11:32:22 AM UTC-7, JJ Sinclair wrote:
> The last day at Montague was spectacular, probably the best soaring day I have ever seen! After flying 7 assigned turn-points in an 8-turn (3hr) MAT, I was 45 miles out with 3500' over MC-3 glide home and the SN-10 said I would be 4 minutes over the 3 hr minimum time. My stats page told me I was doing 70 mph so far after cruising 80 knots all day long.
>
>
>
> Question: Is it faster to raise the MC to 4 or 5 and come home at 90'ish (monitoring time and altitude required), probably bringing my time remaining down to zero..............Or should I use my excess altitude to select another turn-point adding 10 more miles to the total distance and continue to cruise at 80 and be overtime about 13 minutes?
>
>
>
> I did the latter and got 73.5 mph (236 miles), but I have a sneaking feeling I should have done the former.
>
> JJ
OK, I got the E-6B out and answered my own question:
First option (speed up) 226 miles at 3:00 hrs = 75+ mph
Second option (add 10 miles distance) 236 miles taking 3:13 = 73 mph
So, in this example it is 2 miles per hour faster to just speed up and not add extra miles to the total.
Cheers,
JJ
waremark
June 18th 13, 09:07 AM
I think there is a simpler way of knowing the answer. If you can go faster without reducing the time remaining below zero then that will be better.
JJ Sinclair[_2_]
June 18th 13, 02:36 PM
On Monday, June 17, 2013 11:32:22 AM UTC-7, JJ Sinclair wrote:
> The last day at Montague was spectacular, probably the best soaring day I have ever seen! After flying 7 assigned turn-points in an 8-turn (3hr) MAT, I was 45 miles out with 3500' over MC-3 glide home and the SN-10 said I would be 4 minutes over the 3 hr minimum time. My stats page told me I was doing 70 mph so far after cruising 80 knots all day long.
>
>
>
> Question: Is it faster to raise the MC to 4 or 5 and come home at 90'ish (monitoring time and altitude required), probably bringing my time remaining down to zero..............Or should I use my excess altitude to select another turn-point adding 10 more miles to the total distance and continue to cruise at 80 and be overtime about 13 minutes?
>
>
>
> I did the latter and got 73.5 mph (236 miles), but I have a sneaking feeling I should have done the former.
>
> JJ
In this case you are correct, but lets say my accumulated speed was lower but conditions appear to offer a faster leg if I decided to add another turn-point and by flying over the minimum time I would increase my overall speed. Not sure how to make this decision quickly other than a quick guess-t-estimate.
Cheers,
JJ
On Tuesday, June 18, 2013 9:36:25 AM UTC-4, JJ Sinclair wrote:
> On Monday, June 17, 2013 11:32:22 AM UTC-7, JJ Sinclair wrote:
>
> > The last day at Montague was spectacular, probably the best soaring day I have ever seen! After flying 7 assigned turn-points in an 8-turn (3hr) MAT, I was 45 miles out with 3500' over MC-3 glide home and the SN-10 said I would be 4 minutes over the 3 hr minimum time. My stats page told me I was doing 70 mph so far after cruising 80 knots all day long.
>
> >
>
> >
>
> >
>
> > Question: Is it faster to raise the MC to 4 or 5 and come home at 90'ish (monitoring time and altitude required), probably bringing my time remaining down to zero..............Or should I use my excess altitude to select another turn-point adding 10 more miles to the total distance and continue to cruise at 80 and be overtime about 13 minutes?
>
> >
>
> >
>
> >
>
> > I did the latter and got 73.5 mph (236 miles), but I have a sneaking feeling I should have done the former.
>
> >
>
> > JJ
>
>
>
> In this case you are correct, but lets say my accumulated speed was lower but conditions appear to offer a faster leg if I decided to add another turn-point and by flying over the minimum time I would increase my overall speed. Not sure how to make this decision quickly other than a quick guess-t-estimate.
>
> Cheers,
>
> JJ
It's basically the same problem to solve when flying an area task: are you
flying fast enough to make up for diluting the contribution that final glide
makes to your speed? Keep in mind that you're getting a free segment of flight
from your start altitude down to your finish altitude, flown at your final
glide or interthermal speed. The longer the time you spend on course, where
average speed is less than that, the more you dilute that glide.
There are occasions where it makes sense to extend the flight (e.g. you spent a
long time digging out of a hole). More often, it hurts less than you think
to come in a little early. As John Good pointed out to me, don't just slow
up your final glide to use up those couple minutes you'll be early. You
actually get more points by flying faster.
Matt
C-FFKQ (42)
June 18th 13, 09:25 PM
On Tuesday, 18 June 2013 15:27:15 UTC-4, wrote:
> ... More often, it hurts less than you think
> to come in a little early. As John Good pointed out to me, don't just slow
> up your final glide to use up those couple minutes you'll be early. You
> actually get more points by flying faster.
>
> Matt
Okay, I'll bite (probably regret it...) How can you get more points by flying faster in this situation? I'll declare up-front that I'm not a racer, so I might be misunderstanding the rules and scoring.
Whether you slow down and hit the finish at exactly the right time (not over), or fly faster and arrive earlier, you're still scored for the same distance and the same time. Definitely, if you slow too much and cross after the minimum, you lose points, so I would think arriving early guarantees you the best score for the distance (but not "more" points, given a finish at minimum time).
Basic equation of distance / (greater of actual time or minimum task time)
Steve Leonard[_2_]
June 18th 13, 09:54 PM
On Tuesday, June 18, 2013 3:25:24 PM UTC-5, C-FFKQ (42) wrote:
Okay, I'll bite (probably regret it...) How can you get more points by flying faster in this situation? I'll declare up-front that I'm not a racer, so I might be misunderstanding the rules and scoring. Whether you slow down and hit the finish at exactly the right time (not over), or fly faster and arrive earlier, you're still scored for the same distance and the same time. Definitely, if you slow too much and cross after the minimum, you lose points, so I would think arriving early guarantees you the best score for the distance (but not "more" points, given a finish at minimum time). Basic equation of distance / (greater of actual time or minimum task time)
The US rules will score you at some ratio between your actual time on course and the minimum time on course if you are under minimum time, but not more than 15 minutes under minimum time. So, if the minimum task time is 3 hours, the pilot that comes back in, say, 2:54:20 will get a slightly higher speed for the same task distance as the pilot that comes back at 3:00:00. This was done to make it so that you didn't have a tie for everyone who was undertime but hit the same turnpoints. Of course, this was also in the days when if you went to the same turnpoints, you got the exact same distance.. i.e., pre GPS documentation of the flight.
It might pay if you are really early to hang out to be 00:14:59 under time, as opposed to being 00:15:01 under time. Another of those "edges" that a rule defines.
There is another thing that happens in the US rules if you are more than 15 minutes under time. It has to do with potentially reducing the number of points the winner for the day will get if enough of the pilots are more than 15 minutes under time.
Hope that hasn't made your head hurt too much!
Steve
C-FFKQ (42)
June 18th 13, 10:25 PM
On Tuesday, 18 June 2013 16:54:52 UTC-4, Steve Leonard wrote:
> ... Hope that hasn't made your head hurt too much!
> Steve
Thanks, Steve. That does make sense.
Steve Koerner
June 18th 13, 11:51 PM
I'm annoyed with myself that I didn't know this.
Can anybody express this adjustment quantitatively for us? Otherwise, I guess I'll have to ploy through the scoring formula all by my lonesome.
Tony[_5_]
June 19th 13, 02:11 AM
11.6.3.2 For finishers whose TOC is less than MINTIME:
STOC = MINTIME - (MINTIME - TOC) * UTFACTOR
For a Turn-area task:
UTFACTOR = 0.1 + 6 * ((DIST
Steve Koerner
June 19th 13, 03:38 AM
Tony: you clipped off part of the formula but you did point me to the right section which is half the battle; so thanks.
I would summarize the rule like this: The scored time element for determining speed when undertime is 90% based on min time and 10% based on time on course. I didn't see anything about that rule changing for guys that are more than 15 minutes under time as Steve Leonard suggested.
The formula has a provision that further reduces the scored time element if the pilot has flown more than 85% of the maximum task distance. In that case the scale slides between 10% / 90% at and below the 85% threshold to 100% / 0% for the pilot that flies to the very back of every turn area. The effect then is that you are entirely scored based on time on course as long as you go to the very back of all the turn areas. This clearly is intended to keep a valid competition going in the case that the CD has called too short of a task for the prescribed minimum time.
By typing out this summary, maybe I'll be able to remember it for a couple weeks anyway.
JJ: Sorry, I suppose we hijacked your original question. Anyone able to respond to JJ's original question should please do so.
Tony[_5_]
June 19th 13, 03:45 AM
On Tuesday, June 18, 2013 9:38:45 PM UTC-5, Steve Koerner wrote:
> Tony: you clipped off part of the formula but you did point me to the right section which is half the battle; so thanks.
>
>
>
> I would summarize the rule like this: The scored time element for determining speed when undertime is 90% based on min time and 10% based on time on course. I didn't see anything about that rule changing for guys that are more than 15 minutes under time as Steve Leonard suggested.
>
>
>
> The formula has a provision that further reduces the scored time element if the pilot has flown more than 85% of the maximum task distance. In that case the scale slides between 10% / 90% at and below the 85% threshold to 100% / 0% for the pilot that flies to the very back of every turn area. The effect then is that you are entirely scored based on time on course as long as you go to the very back of all the turn areas. This clearly is intended to keep a valid competition going in the case that the CD has called too short of a task for the prescribed minimum time.
>
>
>
> By typing out this summary, maybe I'll be able to remember it for a couple weeks anyway.
>
>
>
> JJ: Sorry, I suppose we hijacked your original question. Anyone able to respond to JJ's original question should please do so.
just in case it matters, my partial copy/paste job was from the 2013 regional sports class rules. I don't know if the Nationals and/or FAI classes use the same formula (they probably do)
Surprise, surprise, I've worked this one out. Lots of free time in the winter I guess...
To restate the question: you're finishing up a flight. You have excess altitude so you're going to be over time. You have a turn area ahead of you or choice of MAT turnpoints, so you can either fly fast but for less distance or short for more distance. What's the optimum?
Think of it as a classic final glide question. But instead of "how do I use up the altitude I have and just make the distance to the finish gate," now the question is "how do I use up the altitude I have and go around one more turn before going to the finish gate?"
It's obviously not either extreme. If you point the nose at the ground and fly VNE, you will add a few miles very fast, but it won't help your average speed much.
And clearly floating along at best LD, 53 knots, won't help your speed if you've been doing 80 all day. So, the optimum is in between. What is it?
Answer: First, figure out the MacCready setting that, in classic climb and glide mode, produces the average speed you have achieved so far. (Intersection of tangent line to the horizontal axis of the polar.) For example in a dry ASW27, in 3 knot thermals, climb and glide MacCready theory says you cruise at 80kts and achieve 54 mph average. So, if you have averaged 54 mph from start to now -- no matter how you did it -- the MacCready setting we're looking for is 3. You do carry around a little card of these numbers, right? (I keep pestering cleanav to put them in but they keep saying things like "John, nobody but you wants this stuff!")
Now, the final glide rule: use a MacCready setting on your final glide equal to this MacCready setting. If you achieved 54 mph from start to now, fly the final glide at MacCready 3, or about 80 knots in a dry ASW27. Set off at 80 knots, turn the glide computer to 3.0, and turn the final turn area when it says you will just make it home.
This is the simple rule to remember, and it's interesting. Classic final glide theory, where you only get to pick how high to climb in the last thermal, says equate the MacCready setting on the way home and the climb rate of the last thermal. Final glide theory when you can set the length of the final glide says to use the MacCready setting on the way home equal to what produced the average speed so far. You would now stay in the last thermal so long as it is stronger than the MacCready setting corresponding to your average speed so far, and then set out at that setting.
If you need a simpler rule, it would be "keep doin' what you've been doin' all along."
The actual formula has an extra term: The real formula is
MacCready setting on final glide = Setting that produces average speed so far +
+ current height / time on course so far.
So you do fly a little bit faster. For most tasks the last term is small. If you're at 6000 feet after a 3 hour task, it's 6000 / (3 x 60) == 33 fpm or 0.3 knots. So the real rule is to fly the final glide at MacCready 3.3, not MacCready 3.0. But we all push final glides a bit anyway, and this isn't a big difference. The accurate formula is more important to answer r.a..s. ers who will say "what if you're at 10,000 feet after a 5 minute task? Then, yes, H/T is huge and you point the nose at the ground and go VNE.
Quiz time: Tuesday June 25. Location: Hobbs NM.
John Cochrane
PS: Here is the table for an ASW 27. Ach is the achieved speed in classic climb and glide flight. stf is the classic speed to fly in knots.
|-----Dry ---||----Wet -----|
Mc stf Ach stf Ach
Kt Kt mph Kt mph
0 56 0 65 0
1 65 32 78 32
2 73 45 89 49
3 80 54 99 59
4 86 61 108 68
6 98 71 124 81
8 108 79 138 92
So, MacCready 3 is 80 knot cruise dry, 99 knot wet, and averages 54 mph dry and 59 mph wet.
If you're at Hobbs (say) ad you have achieved 68 mph so far, then you finish at Mc 4 and 108 knots. And if you've achieved 81 mph so far....
This is all just the very flat polar of modern gliders. Nobody flies that fast, which is a puzzle for another day
John Cochrane
Mike C
June 19th 13, 11:08 PM
On Wednesday, June 19, 2013 3:35:29 PM UTC-6, wrote:
> PS: Here is the table for an ASW 27. Ach is the achieved speed in classic climb and glide flight. stf is the classic speed to fly in knots.
>
>
>
> |-----Dry ---||----Wet -----|
>
> Mc stf Ach stf Ach
>
> Kt Kt mph Kt mph
>
> 0 56 0 65 0
>
> 1 65 32 78 32
>
> 2 73 45 89 49
>
> 3 80 54 99 59
>
> 4 86 61 108 68
>
> 6 98 71 124 81
>
> 8 108 79 138 92
>
>
>
>
>
> So, MacCready 3 is 80 knot cruise dry, 99 knot wet, and averages 54 mph dry and 59 mph wet.
>
>
>
> If you're at Hobbs (say) ad you have achieved 68 mph so far, then you finish at Mc 4 and 108 knots. And if you've achieved 81 mph so far....
>
>
>
> This is all just the very flat polar of modern gliders. Nobody flies that fast, which is a puzzle for another day
>
>
>
> John Cochrane
Very nice of you John.
Thank you.
Mike
Ron Gleason
June 19th 13, 11:36 PM
quiz answer - Start of the 2013 15 Meter shoot out at the Hobbs corral. Great group of pilots. Same for the Open Class and regionals.
Here is hoping for good weather.
Rooting for the UT gun slingers
On Wednesday, June 19, 2013 2:28:57 PM UTC-7, wrote:
> So you do fly a little bit faster. For most tasks the last term is small. If you're at 6000 feet after a 3 hour task, it's 6000 / (3 x 60) == 33 fpm or 0.3 knots. So the real rule is to fly the final glide at MacCready 3.3, not MacCready 3.0. But we all push final glides a bit anyway, and this isn't a big difference. The accurate formula is more important to answer r..a.s. ers who will say "what if you're at 10,000 feet after a 5 minute task? Then, yes, H/T is huge and you point the nose at the ground and go VNE.
> John Cochrane
Thanks John - great grounding back the the original theory. I was going to answer JJ along similar lines until I realized that his calculation was correct. But his calculation told him to not do what he'd been doing, but rather to burn off the altitude by going home at a faster stf than he'd been flying all day. RASers might ask "why is that?".
The answer is that he'd been cruising too slow for the theory all day. I don't have the polar for JJ's awesome bat-plane, but just using your table for the -27, if JJ had been achieving 70 mph then his STF should be 98 mph, so perversely, speeding up the final glide is the right thing to do since he'd been cruising at 80 knots all day. By 90 knots is still less than 98 knots so any final glide less than 98 knots still increases average speed on task versus slower final glide speeds.
The nice thing about the final glide is it's the "equalizer" with respect to McCready theory since your achieved cross-country speed up to the decision point is an absolute determinant as to whether accelerating your final glide will be accretive or dilutive to your speed on task. I think the right procedure here is probably to look at your average speed on task, figure out what is the McCready setting that corresponds to that task speed, then set your glide computer to that McCready and extend or contract the task length (subject to MinTime) to arrive exactly at minimum finish altitude.
9B
Jim White[_3_]
June 20th 13, 10:57 AM
In an AAT points are awarded for speed. Assuming you are always over time:
If you fly further at your average so far you will fly further but no
faster.
If you fly straight to the finish but end up high you have wasted time /
distance and therefore finish at less than potential speed.
So I conclude that flying further only helps if it is done at a
considerably higher speed than your average so far.
My calcs for a 3hr task are as follows:
Scenario is 5000ft left with 50k to go. First 160 mins at 100kph average.
Fly to the finish at 55kts = 100kph 30 mins 100kph average
Fly to finish at 80kts = 150kph 20 mins 105kph average
If you had sufficient height to fly the glide at 120kts = 225kph 13 mins
giving 109Kph average.
Using this height to fly as far as you can at 80kts would not improve this
average speed enough to warrant the additional risk.
For me I would just belt for the finish as flying further introduces risk
of losing time through bad air, or worse a landout etc.
On Thursday, June 20, 2013 4:57:40 AM UTC-5, Jim White wrote:
> In an AAT points are awarded for speed. Assuming you are always over time:
>
>
>
> If you fly further at your average so far you will fly further but no
>
> faster.
>
>
>
> If you fly straight to the finish but end up high you have wasted time /
>
> distance and therefore finish at less than potential speed.
>
>
>
> So I conclude that flying further only helps if it is done at a
>
> considerably higher speed than your average so far.
>
>
>
> My calcs for a 3hr task are as follows:
>
>
>
> Scenario is 5000ft left with 50k to go. First 160 mins at 100kph average.
>
>
>
> Fly to the finish at 55kts = 100kph 30 mins 100kph average
>
> Fly to finish at 80kts = 150kph 20 mins 105kph average
>
>
>
> If you had sufficient height to fly the glide at 120kts = 225kph 13 mins
>
> giving 109Kph average.
>
>
>
> Using this height to fly as far as you can at 80kts would not improve this
>
> average speed enough to warrant the additional risk.
>
>
>
For me I would just belt for the finish as flying further introduces risk
of losing time through bad air, or worse a landout etc.
Jim,
A little harsh, but maybe that's why you don't win contests and BB does...
Steve Leonard[_2_]
June 20th 13, 04:05 PM
On Thursday, June 20, 2013 1:36:14 AM UTC-5, wrote:
> Some snippage...The answer is that he'd been cruising too slow for the theory
> all day.
> 9B
Ah, but theory assumes dead air between climbs. If you cruise in air that is going up, you can average considerably higher speeds than what MC theory says you should be able to achieve for the climb rate you get when you stop to circle.
JJ's question was on a MAT, not a TAT. Difference between them is that you can exactly tune distance on a TAT, where on a MAT, you are step functions to next available turnpoitn on your way home. Also, you will note that JJ said he was already above glide when he discovered he had a final glide decision to make. So, he didn't intentionally climb to that postion, he probably got there cruising under good clouds, making good higher than MC ground speed for the climbs he was taking. But, if it was one of the best days he has seen in a long time, I will agree with you 9B, that he might have had his MC set too low and been cruising slower than optimum for conditions.
As to how to handle that situation on an MAT, as long as your ground speed on the final glide is higher than your achieved speed to that point, you are going to have a very hard time convincing me that you can fly faster overall by flying slower for longer.
Steve Leonard
Long time scoresheet fodder, but sometimes not. Oh, and my best ever daily finish was on a MAT day during the US Open Nationals, 2006. I was just a touch under minimum time.
Jim White[_3_]
June 20th 13, 04:58 PM
At 13:19 20 June 2013, wrote:
>On Thursday, June 20, 2013 4:57:40 AM UTC-5, Jim White wrote:
>For me I would just belt for the finish as flying further introduces risk
>of losing time through bad air, or worse a landout etc.
>
>Jim,
>A little harsh, but maybe that's why you don't win contests and BB
does...
>
Herb, I think you are being unfair. Since your post I have done the calcs
in a spreadsheet (the raw math is too difficult for my little brain).
In the situation I pose BB can fly average better than me at all wing
loadings but here are some examples:
ASW27 50k to go 50k/m wing loading
BB flies at 70kts for 24 minutes avg 103.49kph
I fly a few knots faster striaght to the finish 103.36kph
ASW27 40k to go 50k/m wing loading
BB flies at 85kts for 15.6 minutes average 104.57
I fly a few knots faster 15.3 minutes average 104.47
ASW27 30k to go 50k/m wing loading
BB flies at 90kts for 13.48 minutes average 104.63
I fly at 100kts for 9.73 minutes average 104.36
In all case BB beats me but by less than 0.3% or about 1 point
I have never flown against BB so don't know whether he would beat me on the
day.
Steve Leonard makes the point in support of my suggestion that you do not
fly through still air so BB flying longer has the opportunity to gain more
energy allowing him to go further still. I will too which allows me to fly
faster still.
If you want to check the spreadsheet send me an email and I will forward it
to you to play with.
Jim
On Thursday, June 20, 2013 2:57:40 AM UTC-7, Jim White wrote:
> In an AAT points are awarded for speed. Assuming you are always over time:
>
>
>
> If you fly further at your average so far you will fly further but no
>
> faster.
>
>
>
> If you fly straight to the finish but end up high you have wasted time /
>
> distance and therefore finish at less than potential speed.
>
>
>
> So I conclude that flying further only helps if it is done at a
>
> considerably higher speed than your average so far.
>
>
>
> My calcs for a 3hr task are as follows:
>
>
>
> Scenario is 5000ft left with 50k to go. First 160 mins at 100kph average.
>
>
>
> Fly to the finish at 55kts = 100kph 30 mins 100kph average
>
> Fly to finish at 80kts = 150kph 20 mins 105kph average
>
>
>
> If you had sufficient height to fly the glide at 120kts = 225kph 13 mins
>
> giving 109Kph average.
>
>
>
> Using this height to fly as far as you can at 80kts would not improve this
>
> average speed enough to warrant the additional risk.
>
>
>
> For me I would just belt for the finish as flying further introduces risk
>
> of losing time through bad air, or worse a landout etc.
Okay Jim, it took me a little while to figure out what you were trying to do. Here's my take on your example.
We are assuming a MAT where there are some additional turn options. Steve is right that the distance increments are discrete rather than continuous as in a TAT, but let's assume that there are reasonable options available and you want to pick the optimal one.
The first issue I have with your example is that you are simply calculating for speed over a fixed final glide distance, but you have the option to extend your task distance under a MAT so flying slower and finishing really high hardly seems like the right alternative to test.
Allow me to demonstrate why there is an optimal answer that is equal to the McCready speed corresponding the the average speed achieved up to the final glide.
For your example (using an ASW-27 polar in this case) the McCready setting for 62 mph (100kph) is 4.2 kts. This corresponds to an 88 kt cruise speed. With your 5000' above finish height you can go 27.1 miles at 88 kts in 18.5 minutes, yielding a task speed of 66.2 mph.
If you fly slower at 78 kts, from 5000' above the finish you can go 32.4 miles in 24.9 min. for an average task speed of 65.8 mph. or about a half mile per hour slower, worth about 6 points.
If you fly faster at, say, 98 kts, you can fly 22.6 miles in 13.9 minutes for an average task speed of 66.1 mph.
At 68 kts you can go 37.1 miles and average 64.9 miles
At 108 kts you can go 19.1 miles at 66.0 mph.
The optimal curves are pretty flat and it is slightly less disadvantageous to fly x knots too fast than x knots too slow.
9B
On Thursday, June 20, 2013 9:51:55 PM UTC-7, wrote:
Steve - it is possible to make a better task speed by slowing down in this example. To recap, on a 4.3 kt McCready day when you are averaging 62 mph in cross country speed, you will achieve a better overall task speed by slowing down from any final glide speed in excess of 88 kts and speeding up from any glide speed less than 88 kts. This is simply because the polar is a quadratic curve. The summary table follows.
- At 68 kts you can fly 37.1 miles for a task speed of 64.9 mph.
- At 78 kts, you can go 32.4 miles for a task speed of 65.8 mph.
- At 88 kts, you can go 27.1 miles for a task speed of 66.2 mph.
- At 98 kts, you can fly 22.6 miles for a task speed of 66.1 mph.
- At 108 kts you can fly 19.1 miles for a task speed of 66.0 mph.
9B
Jim White[_3_]
June 21st 13, 09:51 AM
In the UK we fly an AAT where you can turn anywhere you like in defined
areas. I am not sure which US task type this maps onto.
It is received wisdom that you should use surplus height to fly further
into the last area before turning but the spreadsheet turns up a surprise:
you don't gain much unless flying straight home fast brings you in under
time.
On reflection I would slightly modify my rule of thumb such:
If it is a strong day and you have surplus height at a time that allows you
to belt home without taking a time penalty, fly a final glide that takes
you a little further into the area before turning for the finish at the
strong MacCready setting. You would gain a few extra points.
If it is a weaker day (<3kts) then use your surplus energy to fly straight
home as fast as possible consistent with getting there.
It is only worth going for the extra point by extending the distance if you
can still guarantee getting home. Flying a long final glide with a low Mc
is taking unecessary risk.
Jim
9B...I have sent you the SS by email.
On Friday, June 21, 2013 1:51:00 AM UTC-7, Jim White wrote:
> In the UK we fly an AAT where you can turn anywhere you like in defined
> areas. I am not sure which US task type this maps onto.
Jim,
AAT=TAT. The OP was flying a long MAT, which is a US task type where the pilots fly to an assigned sequence of turnpoints (each with a 1 sm turn cylinder). If you are still under time after flying all assigned turns you can add additional turnpoints of your choosing. For the purposes of this discussion MAT and TAT (or AAT) are roughly equivalent, the only difference being that under a MAT the distance increments you can add are not infinitely variable as in the TAT but rather come in discrete chunks. Generally there enough close in turnpoint options to use up whatever altitude you have and if you hit the finish cylinder first you even have an insurance policy of a provisional finish in the event you land out while adding distance (you mention this risk later).
You rule of thumb makes sense to me.
Ideally you set the Mc for final glide at the Mc that corresponds to the task speed that you have achieved. However there is a lower limit if you want to mange landout risk. I rarely set my final glide for less than Mc = 4. There are only a handful of points at stake from flying faster than optimal McCready and coming up short on a final glide is very costly should you get even small amount of unanticipated sink on a very flat final glide.
> 9B...I have sent you the SS by email.
Never got the SS
9B
A simpler summary.
First, don't think speed, think MacCready setting. The basic principle is, finish the flight at the MacCready setting that generates your average speed so far.
So, you adapt to lift and sink accordingly. If you have averaged Mc 3 so far, and you run in to 4 knots lift, take it and extend the flight some more. As long as you find Mc 4 thermals and cruise accordingly you are going to increase your average speed.
Yes, the tops of hills are flat. And this does not include the risks of landout. All that shades toward higher and faster.
John Cochrane BB
kirk.stant
June 21st 13, 07:30 PM
For us knuckle-draggers that can't quite wrap our brain cells around MacCready speeds in real time, I thought that the simple way to look at it was: If going over time is going to raise your average speed (i.e. a beautiful cloud street shows up at the end of a slow day) then extend as long as it is helping your average speed. Otherwise, finish just above min time on a normal (fading) day.
Without a handy chart of XC speed vs MC settings for my glider, all I got is my SN10's handy Average Speed display, which is what I use to decide whether I can make the number get bigger or smaller.
Ouch - math in the cockpit!
Kirk
66
On Friday, June 21, 2013 2:30:30 PM UTC-4, kirk.stant wrote:
> For us knuckle-draggers that can't quite wrap our brain cells around MacCready speeds in real time, I thought that the simple way to look at it was: If going over time is going to raise your average speed (i.e. a beautiful cloud street shows up at the end of a slow day) then extend as long as it is helping your average speed. Otherwise, finish just above min time on a normal (fading) day. Without a handy chart of XC speed vs MC settings for my glider, all I got is my SN10's handy Average Speed display, which is what I use to decide whether I can make the number get bigger or smaller. Ouch - math in the cockpit! Kirk 66
Knuckle Draggers!
I (rep)resent that remark.
LOL
This is a good description of what I do, even if I don't beat BB all that much.
UH
OK, time to come clean. I don't do a lot of math in the cockpit either. This kind of exercise is useful as a general guide -- no, if you're over time it is not a good idea to fly off 14000' at VNE. And it's useful to adapt to unusual circumstances. But in practice flying in good air is more important than anything else, and I spend most of my energy looking out the window to figure out where the good air is and the gliders aren't.
John Cochrane
On Friday, June 21, 2013 11:30:30 AM UTC-7, kirk.stant wrote:
> For us knuckle-draggers that can't quite wrap our brain cells around MacCready speeds in real time, I thought that the simple way to look at it was: If going over time is going to raise your average speed (i.e. a beautiful cloud street shows up at the end of a slow day) then extend as long as it is helping your average speed. Otherwise, finish just above min time on a normal (fading) day.
That's funny Kirk - the goal is to ensure that your knuckles don't drag on final glide!
The answer to your question is yes.
The way you manage it is with the McCready dial on your SN-10 and the turnpoint position (for a TAT), or turnpoint selection (for a MAT). You set the McCready to the setting that corresponds to the task speed achieved so far and adjust the final glide distance to have the arrival height you want. If you are in a cloud street, keep flying as long as you can maintain that final glide speed and are above your minimum arrival height (or think you can reach it without slowing down).
It does help to have a version of John's table to guide you, because in my experience I tend to cruise on course at a lot lower speed than the recommended McCready STF so I need to judge versus the optimal glide speed, not the one I've been flying to stay higher, follow lift bands, etc.
If you don't know how to make a table, send me three points off your LS-6 polar (dry), your max water ballast capacity and I'll email you one you can print out.
9B
kirk.stant
June 21st 13, 10:04 PM
On Friday, June 21, 2013 3:12:13 PM UTC-5, wrote:
> The way you manage it is with the McCready dial on your SN-10 and the turnpoint position (for a TAT), or turnpoint selection (for a MAT). You set the McCready to the setting that corresponds to the task speed achieved so far and adjust the final glide distance to have the arrival height you want. If you are in a cloud street, keep flying as long as you can maintain that final glide speed and are above your minimum arrival height (or think you can reach it without slowing down).
Interesting idea, I'll have to try it next time. So far, I just use the recommended speed for the MC to try to fly a good ballpark speed (I hate the speed director and try to avoid fancy push-pulls), then look at the acheived XC speed when deciding on final glide tactics - it's usually pretty easy to figure out if it's going to get faster or slower...
Just for grins, I did a quick comparison of my flights during R9 at Moriarty, comparing them to BB's chart. My 6 was at 10psf every flight, and without draglets I figure it's pretty close to a 27 ;^).
Day 1 I got spooked by a big storm over the field so took way too much time getting home and the numbers show it, but the remaining 3 days are interesting:
Day 1 Avg climb 3.8 knots, XC speed 59 mph, BBs MC 4 (wet) XC speed s/b 68 mph.
Day 2 Avg climb 5.3 knots, XC speed 75 mph, BBs MC 5 (wet) XC speed s/b 74 mph.
Day 3 Avg climb 5.6 knots, XC speed 80 mph, BBs MC 6 (wet) XC speed s/b 81 mph.
Day 4 Avg climb 5.2 knots, XC speed 73 mph, BBs MC 5 (wet) XC speed s/b 74 mph.
Pretty close match. Looking at my actual cruise speeds, they are in the ballpark of the speeds suggested by the chart, with the average a bit lower (working lift bands) but a lot of time higher.
Darned it that fancy math stuff kinda works!
By the way, the skies south of Chicago looked AWESOME yesterday! Unfortunately, I was looking at them from my car...
Cheers,
66
66
>
>
> By the way, the skies south of Chicago looked AWESOME yesterday! Unfortunately, I was looking at them from my car...
>
>
>
> Cheers,
>
> 66
>
Feel better. I was out at the airport getting the glider ready and doing some instructing. Big mushburger clouds with not much in them. A very interesting line formation and nw curl over light south flow... but no big excitement in the air.
John Cochrane BB
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